1. Field of the Invention
This invention relates to a method for peeling a film attached on the surface of a semiconductor wafer or, in particular, to a film peeling method for peeling a surface protective film attached on the surface of a very thin semiconductor wafer and a film peeling apparatus for carrying out the method.
2. Description of the Related Art
In the first half of the semiconductor fabrication process, the periphery of the semiconductor wafer is chamfered to prevent cracking, cuts or dust during the semiconductor fabrication process. Normally, the semiconductor wafer is chamfered during the semiconductor wafer fabrication process. Semiconductor wafers chamfered and ground so as to have a mirror-finished surface are supplied as a material to the first half of the semiconductor fabrication process.
In chamfering the semiconductor wafer, the upper and lower edges of the semiconductor wafer are ground into a taper using a grinding stone or the like, and polished. A circuit element is formed on the surface of the semiconductor wafer chamfered in this way. The trend in the semiconductor fabrication field is toward larger semiconductor wafers. In order to increase the mounting density, on the other hand, the thickness of semiconductor wafers has continued to decrease. A back grind process for grinding the back surface of the semiconductor wafer is conducted to reduce the thickness of the semiconductor wafer. The back grind process has recently reduced the thickness of semiconductor wafers to 100 μm or less. Further, the research and development efforts are aimed at providing a thickness of 50 μm or less. Before the back grind process, a surface protective film for protecting the circuit element is attached to the front surface of the wafer.
The back grind process is a process to extremely reduce the thickness of the semiconductor wafer, and therefore, during the back grind operation, the peripheral portion of the wafer is liable to be cracked or cut. Especially, a semiconductor wafer thickness not larger than 100 μm results in a lower mechanical strength of the semiconductor wafer and cracking or cuts can occur.
The surface protective film attached to protect the circuit element formed on the front surface of the semiconductor wafer is required to be peeled after the back grind process. In the prior art, a peeling tape is attached over the whole of the surface protective film of the semiconductor wafer by an application roller, and after attaching and bonding the peeling tape on the surface protective film, the peeling tape coupled with the surface protective film is wound off thereby to peel off the surface protective film.
The very thin semiconductor wafer after the back grind process, however, is greatly reduced in mechanical strength and, therefore, a problem is posed that the semiconductor wafer can be broken when attaching the peeling tape on the surface protective film. Further, the semiconductor wafer may be broken during the peeling process.
In order to solve these problems, Japanese Unexamined Patent Publication No. 2004-165570 discloses a method in which the direction of the semiconductor wafer is adjusted in such a manner that the direction of the peeling tape fails to coincide with the dicing grooves formed on the semiconductor wafer. Also, Japanese Unexamined Patent No. 2004-128147 discloses a peeling device in which the peeling operation is started from a corner of the semiconductor wafer.
After the back grind process, the thickness of the semiconductor wafer is considerably reduced, and therefore the back surface of the semiconductor wafer subjected to the back grind process is attached on the dicing tape, then the dicing tape is fixed on a frame slightly larger than the semiconductor wafer. Thus, the handling of the semiconductor wafer is facilitated.
After that, the semiconductor wafer is supplied to the peeling device together with the frame. In the peeling device, the peeling tape is attached on the surface protective film by a peeling member, and then the peeling member is moved along the surface of the semiconductor wafer so that the surface protective film is peeled.
As described in Japanese Unexamined Patent No. 2004-165570, the thickness of the semiconductor wafer is considerably reduced and the edge of the semiconductor wafer is formed as a chamfered portion. The peeling member pressed against the edge of the semiconductor wafer mounted on a frame via the dicing tape may slip off from the chamfered portion. In such a case, the peeling tape of the peeling member and the dicing tape may stick to each other, with the result that a peel starting point may not be appropriately formed. Also, if the peeling member attached to the dicing tape is forcibly separated, a large force is applied on the edge of the wafer and the wafer can be broken.
This invention has been achieved in view of the aforementioned situation, and the object of the invention is to provide a film peeling method and a film peeling apparatus for carrying out the method, in which a peel starting point of the surface protective film can be easily formed in order to prevent cracking or cutting of the forward end of the semiconductor wafer which otherwise might be caused at the time of starting to peel the surface protective film.